A blasting process using explosives is frequently carried out for construction and engineering operations, in particular, underground tunnel excavation. Although the blasting process has the merit of being capable of efficiently removing a rock base or other obstacles using the explosive power of the explosives, vibration and noise that are unavoidably produced upon blasting are propagated to the ground surface, having an adverse effect on buildings and a variety of other structures. In addition, although impact waves propagated from the source of explosion during the blasting process are significantly reduced depending on the distance, some of the energy generated at that time causes vibration (blast vibration) of the ground while being propagated in the form of elastic waves. When a building or subway facilities are present at a relatively close distance from the source of explosion, there is a possibility that a severe problem can be caused.
Technologies of the related art for reducing the above-described blast vibration are as follows. First, an excavation structure and method for blocking blast vibration using line drill holes disclosed in Korean Patent No. 0531985 proposed a technology of forming at least two rows of line drill holes around an area to be blasted in a rock base to be excavated such that the line drill holes of one row alternate with the line drill holes of the other row. In addition, a tunnel blasting method disclosed in Korean Patent No. 0599982 proposed a technology that uses large uncharged holes which are formed at a distance from the contour of a tunnel, crack guide holes which are disposed between the uncharged holes, and a plurality of expansion holes which are formed inward of the uncharged holes.
These preceding technologies share a commonality in that a plurality of holes which are formed in the direction in which the tunnel extends is used as a vibration reducing means. However, when a plurality of holes is formed, connecting areas are present between the holes. Blast vibration that is propagated through the connecting areas is not blocked. Therefore, the holes used in the preceding technologies are an imperfect vibration reducing means.
In addition, tunnel excavation methods of the related art leave a damage zone in an adjacent rock base portion due to blasting, thereby causing a danger of the tunnel collapsing (see FIG. 21). In particular, when blast force is excessive, a space exceeding a designed tunnel space is dug, thereby causing overbreak. In this case, a large amount of shotcrete must be poured into the vacant space, which is problematic. In contrast, when blast force is insufficient, underbreak occurs, and an additional operation using an excavator or a rock drill is required.
The tunnel excavation process of the related art involves forming a plurality of charge holes using a jumbo drill, charging the holes with explosives, and exploding the charged explosives. About one hundred charge holes are required for one blasting operation, and the operation of forming the charge holes is manually carried out by jumbo drill workers. Therefore, an improvement in the efficiency of the operation is required.
In general, in the tunnel excavation, a variety of front predictive methods of inspecting the status of a rock bed in the front area that is to be excavated in order to prevent the tunnel from collapsing or the like are being introduced. However, indirect inspection, such as the measurement of a resistance depending on the properties of the rock base, is carried out instead of substantial inspect. Therefore, these methods have low inspection reliability, and still have a danger in that the tunnel may collapse during excavation.